Rubberlike multipolymers prepared from mixtures including a conjugated diene hydrocarbon



Patented Sept. 11, I945 RUBBERLIKE MULTIPOLYMERS PREPARED FROM MIXTURES INCLUDING A CON- JUGATED DIENE HYDROCARBON Waldo L. Semon,

Silver Lake, Ohio, assignor to The B. F. Goodrich Com many, New York, N. Y.,

a corporation of New York hi Drawing. Application January 10, 1942, Serial No. 426,840 r 18 Claims.

Thi application is a continuation-in-part of my copending application Serial No. 322,383 filed March 5, 1940, and relates particularly to rubberlike multipolymers prepared by the polymerization of a mixture containing a conjugated diene hydrocarbon, an. acrylic ester and an acrylic nitrile.

My copending application, referred to above, discloses that extremely valuable synthetic rubbers which are plastic and easily worked in the unvulcanized state and are mechanically strong and chemically resistant in the vulcanized state,

may be obtained by polymerizing a mixture of tnonomeric materials containing a conjugated diene hydrocarbon and at least two other polymerizable materials which are members of the broad class consisting of acrylic esters and nitriles.

It has now been found that certain multipolymers, within this broad class, which are prepared from mixtures containing a conjugated diene hydrocarbon and at least two other 'poiymerizable materials one 01' which is an acrylic nit-rile and another of which is an acrylic ester of the formula wherein R1 is hydrogen or alkyl and Re is a hydrocarbon group, possess certain additional properties which make them particularly valuable synthetic rubbers. Thus, in addition to being plastic, soluble, and easily worked when unvulcanized and to being strong and resistant rubber-like materials when vulcanized, these multipolymers possess the important property of being flexible at temperatures much lower than the temperatures at which other rubber materials stifl'en and become br ttle. They are, therefore, of great value in automotive and aircraft applications where extremely low temperatures are encountered. Moreover, these multipolymers retain the excellent oil resistance characteristics of the two component copolymers of conjugated ,dienes and acrylic nitriles.

The particular compounds and their respective proportions present in the mixtures which are polymerized to form these valuable multiploymers may be varied considerably. It is essential, however, that at least three polymerizable constituents be present in the mixture, namely (1) a conjugated diene hydrocarbon of the formula cH;=c-o=cn R 11 wherein R is hydrogen or methyl such as butalike and (3) an acrylic ester of the formula CHr-=CCOR1 wherein R1 represents hydrogen or alkyl and R2 represents a hydrocarbon group. Suitable acrylic esters of this type include the alkyl acrylates wherein R1 is a hydrogen and R2 is alkyl, such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, butyl acrylate, amyl acrylate, hexyl acrylate, 2-ethyl hexyl acrylate, n-octyl acrylate, duodecyl acrylate and the like; similar alkyl esters of alkyl substituted acrylic acids, wherein R1 is alkyl and R2 is alkyl, such as methyl methacrylate, ethyl methacrylate, ethyl ethacrylate, methyl alpha-butylacrylate and the like; and other esters of this type, wherein R1 is hydrogen or alkyl andRz is some other hydrocarbon group, such as cyclohexyl acrylate, methallyl acrylate, allyl methacrylate, benzyl acrylate and the like. It is also essential that the mixture to be polymerized contain at least" 50% by weight of a conjugated diene hydrocarbon or of a mixture of conjugated diene hydrocarbons.

The preferred multipolymer are those prepared from mixtures containing at least 50% by weight of a conjugated diene, at least 5% by weight of an acrylic nitrile and at least 5% by v weight of an alkyl acrylate. Particularly, the multipolymers prepared from mixtures containing from 50 to by weight of butadiene, from 10 to 40% by weight of acrylonitrile and from 10 to 40% by weight of an alkyl acrylate containing less than 10 carbon atoms in the alkyl group have been found to possess the most valuable properties. It is to be understood, however, that valuable synthetic rubbers possessing flexibility at low temperatures may be prepared from any mixture of polymerizable materials containing at least 50% by weight of at least one conjugated diene hydrocarbon, at least one acrylic nitrile and at least one acrylic ester of the above described type. It is also to be understood that the mixture may contain, in addition to one or more specific compounds in each of the three above mentioned essential types of' compounds, other polymerizable materials such as vinyl compounds, styrene, chloroprene, etc.

In the practice of this invention, the polymerization of these monomer mixtures to form synthetic rubber is preferably carried out in acne- 2 ous emulsion although other polymerization methods such as polymerization in homogenous system by the action of heat, light, pressure or catalysts may also be employed. In the emulsion polymerization process the mixture of monomers is emulsified in water by the use of a suitable emulsifying agent to form an aqueous emulsion to which is added, preferably, one or more polymerization initiators to start the polymerization reaction, one or more polymerization acceleran age resistor or antioxidant such as phenyl beta naphthylamine and is then coagulated by the same methods used to coagulate natural rubber latex, for example, by addition of acid, al-. icohol or salts or by a combination of these methods. Washing and drying of the coagulum produces a crude synthetic rubber which re-' sembles crude natural rubber in appearance and in properties.

The preferred emulsifying agent'for use in the above process consists of a water soluble soap derived from a fatty acid containing between and carbon atoms, such soaps as the sodium or potassium salts of lauric. myristic, palmitlc, oleic or stearic acids being quite suitable. It is usual y desirable to employ the soap as an aqueous solution containing some free fatty acid. that is to emulsify the monomerswith an aqueous solution containing a fatty acid which has been 70 to 95% neutralized with alkali, but it is also possible to employ solutions of soap which are completely neutralized or even solutions of soaps containing P lymerization is 40 disp rsion is then free alkali. Moreover, other emulsifying agents 7 such as salts of organic bases containing long carbon chains, for example trimethyl cetyl ammonium sulfate, or alkali metal alkyl sulfates, for. example, sodium lauryl sulfate, and aryl sulfonates, for example, sodium isobutyl naphthalene sulfonate, may also be employed.

Polymerization initiators which may be used in a the emulsion polymerization process include the D -oxygen type compounds (sometimes called P lymerization catalysts) such as hydrogen peroxide, benzoyl peroxide, ammonium persulfate, sodium perborate, potassium persulfatf potassium percarbonate and the like as well as other types of initiators such potassium diazomethane disulfonate and triphenylmethyl azobenzene. The preferred polymerization accelerators, or catalysts, are heavy metal compounds which are added in small amounts to the emulsion either as simple ionizable heavy metal salts such as ferrous sulfate, cobalt chloride, nickel nitrate or the like. as disclosed in the copending application of William D. Stewart, Serial No. 379,712. filed February 14, 1941, or in form of a redox system comprising a heavy metal i r i complex combination or otherwise associated with some other material such as sodium pyrophosphate, levulinic acid, glycine, cystine, betamercaptoethanol, quebrachitol and cholesterol. as disclosed in the copending applications of William D. Stewart, Serial No. 379,713 to 379,717 filed l 'ebruary 14, 1041. Polymerization modifiers which are also preferably present during the polymerization are usually sulfur containinlmanlc as diazoaminobenzene. di- I butadiene,

assae'n like.

Other polymerization initiators, catalysts, accelerators and modifiers as well as other substances variously known as polymerization regulators, promoters, etc.,

which enable the polymerization to be carried out in a shorter time and at a lower temperature and/or which in some manner improve the quality of the products obtained may also be included in the emulsion before polymerization. All of these added substances are-mentioned only to indicate that best results are obtained when one or more of them are present, and it is not to be inferred that the monomer mixtures may not be polymerized in their absence.

The method of preparing the multipolymers of this invention and the properties which they pos-' sess may further be illustrated by thefollowing specific examples in which the parts, unless otherwise indicated, are by weight.

Example I A monomeric mixture consisting of. 55 parts of parts of acrylonitrile and 20 parts methyl acrylate is emulsified with about 250 parts of a 2% aqueous solution of myristic acid, which drogen peroxide, as a polymerization initiator, 1.0 part of sodium ferri pyrophosphate, as a polymerization accelerator, and 0.6 part of d isopropyl dixanthogen, as a polymerization modifier, are then added to the emulsion and the emulsion is agitated at a temperature of C. After 22 hours the persion is form A small amount of phenyl beta naphthylamine is added to the dispersion and the coagulated with a salt solution. A rubber-like multipolymer resembling crude natural rubber is thus obtained. The multipolymer is plastic, may'be milled and otherwise processed without diificulty and is easily and completely soluble in benzene and acetone. It may be compounded with pigments, softeners, vulcanizing ingredients, etc., in substantially the same manner as natural rubber.

When this multipolymer is compolmded in a standard tire tread recipe and then vulcanized I an excellent vulcanizate is obtained. It possesses a tensile strength of over 4000 lbs. and an ultimate elongation of about 750%. When exposed to low temperatures it remains soft and flexible at temperatures as low as C. Moreover, it possesses excellent oil resistance, undergoing only a 14% volume increase when immersed in mineral oil for two weeks at 80 C.

A two component copolymer at 55 parts butadi'en'e and parts acrylonitrile prepared in identically the same manner does 'not possess these valuable properties. It, for example, is much less plastic, more diifioult to mill and is only about 65%-s0lub1e in benzene or acetone. Moreover, its

vulcanizate becomes brittle at a temperature of only 17.5' C.

Example 11 The following monomer mixture Percent by .weight Butadiene Acrylonitrile 40 Ethyl aerylate 5 is polymerized as in lt'xample I, to form asyntbetic rubber which is plastic and soluble and complete and a latex-like disyields a vulcanizate having a. very low freezing t ming as much 88 ut y B t 0 8 point. A comparison with the 55/45 butadiene conjugated diene hydrocarbon 01' the formula acrylonitrile copolymer follows: cm=0-c=cn Sol i s 5 wherein each R represents a member of the class consisting of hydrogen and methyl, as much as about 5% by. weight of acrylonitrile, and as much Percent C 55/45 butadiene acrylonitrile copolymer..- 68 17.5 as about by ght of an ac y ester of the 55/40/5 butadiene acryionitrile ethyl acryfonnula late multipolymer 100 26 The oil resistance and tensile properties of the two materials are both excellent and are substantially the same.

wherein R2 is a hydrocarbon radical containing no more than 12 carbon atoms. Example In 2. The process which comprises polymerizing in aqueous emulsion a monomer mixture containing A p ymer 15 prepared, as in Ex p from about 50 to 80% by weight or a conjugated from a monomer mixture containing 55% by diene hydrocarbon f the formula weight of butadiene, 15% by weight of acryloni- CH trile and 30% byvweight of butyl acrylate. In F 40 hours an 88% yield of a. plastic soluble syn- R thetic rubber which has an extremely low freezing wherein each It represents a member of the class point, namely --55 C., is obtained. The tensile consisting of hydrogen and methyl. from about properties and oil resistance 0! its vulcanizate are 10 to 40% by weight of acrylonitrile and from also excellent. about 10 to 40% byweight of an acrylic ester of Example IV the formula A mixture containing: cmflikcigmoqzl Parts H Butadiene 55 wherein R: is a. hydrocarbon radical containing Acrylonitrile 20 no more than 12 carbon atoms. Methyl methacrylate 20 3. The process which comprises polymerizing in aqueous emulsion a monomer mixture containare polymerized as in Exampl 1} A plastic 80111- ing from about 50 to 80% by weight of butadieneble synthetic rubber which yields vulcanizates 13} from about 10 t by weight of mhaving a low freezing point and excellent mechant u and from b t 10 t 40% by weight of an ical propertiesis obtained. alkyl acrylate containing less than 10 carbon atoms in the ailwl group. Example V 40 4. The process which comprises polymerizing l in aqueous emulsion a monomer mixture contain- A multipolymer is prepared by the polymerization in aqueous emulsion of a mixture containing 2:22 m g f g gg f iy 35 ufifsg igi: 75% by weight of butadiene' 15% by weight of tril e and from about 10 to 407 by weight or acrylonitrile and 10% by weight of butyl methmethyl mate acrylate. This multipolymer is plastic and solu- 5 The proces's which comprises polymerizing it possesses 10w freezing point and it may in aqueous emulsion a, monomer mixture containbe vulcanized to form excellent vulcanizates.

. ing from about to 80% by weight of butadiene- Example W 1,3, from about 10 to 40% by weight of acryloni- 5 trile and from about 10 to 40% by weight of ethyl Example IV is repeated except that benzyl acry acrylatelate is employed in place of methyl methacrylate. The processs which comprises polymerizing A good yield of a synthetic rubber having pmmb in aqueous emulsion a monomer mixture containties substantially equivalent to the rubber dein? from about 50 t0 by Weight 01' butadienescribed in Example IV is obtained; 1.3, from about 10 to 40% by weight 01' acrylonitrile and from about 10 to 40% by weight of butyl Exampie VII acrylate. Example IV is again repeated except that meth- The Process which comprises polymerizing allyl methacrylate is employed in place of methyl 1n 9411180115 emulsion in the P c f an emulmethacrylate. A good yield of a plastic, soluble slfyms agent. apolymerizetlon n t at r. a polysynthetic rubber is obtained. This synthetic rubmerization catalyst and a e i ation modifier her is also flexible at low temperatures amryrelds a monomer mixture containing from 50 to 80% strong resistant vulcanizates. y weight of butsdiene-m, from 10 to 40% by The above specific examples have been cited Weight of c y nitrile and from-10 to 40% by only for purposes of illustration and it is not into Weight o m hyl ac ylatetended tnat the invention be limited solely there- The p s w ch co prises polymerizing by for it is to be understood that wide variation n aqueous emulsion in the presence of an emulin the nature and proportions of the materlals- 'flfying en a polymerization initiator, a Po polymerized and in the polymerization conditions m rization catalyst and a polymerization modifier employed may be effected without departing from a monomer mixture containin from 50 to 80% the spirit and scope or the invention as defined by weight or butadiene-L3, from 10 to 40% by by the appended claims. weight of acrylonitrile and from 10 to 40% by I claim: weight 01' etl yl acrylate. 1. The process which comprises subjecting to 9. The process which comprises polymerizing polymerizing conditions a monomer mixture con in aqueous emulsion in the presence of an emulsityi x alcnt, a polymcriitflfln initietor, a poly- 14. A rubber-like multipolymer prepared by the merizatlon catalyst and a polymeriation modifier process of claim 5. a. monomer mixture containing from 50 to 80% 15. A rubber-like mu ltipolymer prepared by the by weight oi butndlene-1.3,i'r0m 10 to 40% by process of claim a. 1 weight of aerylonitrile and from 10 to 40% by 5 16. Arubber-like multipolymer prepared by the weight of butyl acrylace. process of claim 7.

10. A rubber-like multipolymer prepared by the 17. A rubber-like multipolymer prepared by the proceae of claim 1. process of claim 8. I

11. A rubber-like multipolymer prepared by the 18. A rubber-like multipolymer prepa ed by t process of claim 2. m process of claim 9. 12. A rubber-like multlpolymcr prepared by the process of china 8.

13. A ruhber-likemultipolymer prepared by the process of claim 4.

WAL'DO L. SEMON. 

